Artificial hydraulic ankle joint

ABSTRACT

An artificial ankle joint with an articulate connection between the foot part and the lower leg part of an artificial leg. A damping device comprising at least two hydraulic cylinders connected by conduits and each provided with a piston is hinged to the foot part and the lower leg part, respectively. The pistons have hollow chambers filled with storage oil and pressure-balancing channels lead to the upper end of the hollow chambers. Between the pressure chambers of the hydraulic cylinder and the hollow chamber of the piston a snifting valve is provided which sucks hydraulic liquid from the hollow piston chamber.

United States Patent [1 1 Karas 1 Mar. 18, 1975 ARTIFICIAL HYDRAULICANKLE JOINT Primary ExaminerRonald L. Frinks 75 I W If K V A t mentor 0gang aras lenna' us nd Attorney, Agent, or Firm-Stemberg and Blake [73]Assignee: Forschungsinstitut fur Orthopadie-Technik, Vienna, Ausma 57ABSTRACT [22] Filed: Apr. 4, 1974 An artificial ankle joint with anarticulate connection [21] Appl 458049 between the foot part and thelower leg part of an artificial leg. A damping device comprising atleast two [30] Foreign Application Priority Data hydraulic cylindersconnected by conduits and each Mar. 8, 1974 Austria 1928/74 Providedwith a Piston is hinged to the foot and the lower leg part,respectively. The pistons have hol- 521 U.S.Cl. 3/1.2, 3/30 10W chambersfilled Wlth Storage 011 and Pressure- [51] CL A6 U00 A6lf H04 A6 H08balancing channels lead to the upper end of the hol- [58] Field ofSearch 3/12, 30-35 10W Chambers- Between the pressure chambers of thehydraulic cylin- [56] References Cited der and the hollow chamber of thepiston 21 snifting UNITED STATES PATENTS valve is provided which suckshydraulic liquid from 2.470.480 5/1949 F H 3/l.2 the hollow istonchamber. 2.657.393 ll/l953 Hz ilir 3/l.2 p

FOREIGN PATENTS OR APPLlCATlONS 5 Claims, 2 Drawing Figures 818328l0/l95l Germany 3/l.2

PATENTEU 3.8711132 sum 2 OF 2 FIG? . ARTIFICIAL HYDRAULIC ANKLE JOINTThe present invention relates to an artificial ankle joint with anarticulate connection between the foot part and the lower leg part of anartificial leg and provided with a damping device hinged, on the onehand, to the foot part and, on the other hand, to the lower leg part,which device comprises two or more hydraulic cylinders connected byconnection conduits and each cylinder being provided with a piston.

Known artificial ankle joints of this kind have the disadvantage that onaccount of the high pressures occurring in the pressure chambers of thehydraulic cylinders, problems as to the tightness arise, which lead tothe gradual loss of hydraulic liquid. Consequently after a short timethere is a play between the moveable parts, which impairs the usabilityof the prosthesis. A further problem in known artificial ankle joints isthe connection of the foot part with the lower leg part, which hashitherto been achieved by connecting-rod joints, which however take upmuch space, are heavy and technically complicated.

Other problems of known artificial ankle joints result from thetemperature dependence of the hydraulic medium, as the viscosityproperties vary strongly with the temperature.

The invention aims at avoiding the above mentioned difficulties anddisadvantages and sets the task of providing an artificial ankle joint,in which the hydraulic medium is automatically replenished; in which theconnection between the lower leg part and the foot part is achieved in atechnically simple and reliable manner and which is widely independentfrom temperature fluctuations.

The aims of the invention in an artificial ankle joint of the abovedescribed type are achieved in that the pistons are hollow, the hollowchambers are filled with storage oil and pressure-balancing channelsbeing in contact with the surrounding atmosphere lead to the upper endof the hollow chambers, wherein a springloaded snifting valve isprovided between the pressure chamber of the hydraulic cylinder,respectively the hollow chamber of the piston, preferably in the bottompart of the latter.

Preferably the lower leg part is provided with two rollers of equaldiameter, arranged symmetrically in relation to the joint, which rollersare connected by a tension spring with the pistons of two equallydimensioned hydraulic cylinders arranged parallel, each piston beingheld in contact with the rollers by the tension springs.

Suitably the pistons are supported by means of a tappet on the rollers,the tappets having roll-off surface acting against the roller surfaces.

According to a preferred embodiment of the invention throttle valveswith obstacles for ensuring a permanently turbulent flow are installedin the connection conduits of the hydraulic cylinders.

The subject of the invention will now be described in more detail by wayofexample with reference to the accompanying drawings.

FIG. I is a vertical section through the artificial ankle joint and FIG.2 is a section along line "-11 of FIG. 1.

According to FIG. I the artificial ankle joint, comprises, according tothe invention, two cylinders 2 and 3 borne in a common housing andhaving parallel axes, in which cylinders pistons 4 and 5 are guided. Thepressure chambers of the cylinders are connected with each other byconnection conduits 6, 7 (FIG.,2) which conduits are bored into thecontrol block 8. which is flanged to the upper side of the housing. Inthe connection conduits 6, 7 throttle means are provided. The housing 1is connected, on the one hand, with the foot part 10 via the joint 11and, on the other hand, with the lower leg part 12 via the screw 13. Thetwo axially parallel hydraulic pistons 4, 5 of equal size are providedwith tappets 14, 15, which are supported by rollers or rolls 16, 17respectively of equal diameter arranged symmetrically in relation to theaxis of the joint 11. Tension springs 18, 19 which partly surround therol lers, are secured to the pistons, so that the pistons are alwayskept in their lowest position and the bottom surface of the tappet ispressed against the peripheral surface of the rollers. Thus the bottomsurfaces of the tappets roll off the peripheral surfaces of the rollersand a connecting-rod-type movement is imitated.

The pistons 4, 5 are hollow, the hollow chambers serving as storagecontainers for hydraulic liquid. They are filled with hydraulic liquidalmost as far as the upper end (which is however not illustrated for thesake of better clarity). From these storage chambers hydraulic liquid issupplied, which is partly consumed during use in any hydraulic devicefor lubrication. For the purpose of supplementing the hydraulic liquid apressure-balancing tube 20 is arranged in each piston, which tube is incontact with the surrounding atmosphere and reaches almost as far as theupper end of the chamber of the piston. At the front-side of the pistona snifting valve 21 is installed, which reaches close to the bottom ofthe piston. In the tube a valve body 26 is guided, on which a weakpressure spring 25 acts, which valve body is downwardly sealed off byseals 27. Into the upper end of the tube a worm screw 28 is inserted, bymeans of which the prestress of the spring may be altered.

When by the occurence of a leakage or on account of the normal loss ofhydraulic liquid caused by the use of the prosthesis there is a playbetween the tappet and a roller, underpressure is caused in the cylinderand the missing quantity of liquid is sucked from the hollow pistonchamber via the snifting valve.

At the given conditions, i.e., at the existing piston velocities and ata low quantity of hydraulic liquid being in flow very small Reynoldsfigures occur in the connection conduits of the hydraulic cylinders.This may lead to difficulties, as the viscosity properties of thehydraulic medium vary on account of the dependence on the temperature.In order to avoid this disadvantage, throttle valves are providedaccording to the invention in a particular manner in the connectionconduits so as to guarantee a permanently turbulent flow. This isillustrated in more detail in FIG. 2.

Each connection conduit, respectively each overflow channel 6, 7 in thecontrol block 8, contains a reflux valve 29 and a throttle valve 30, theflow direction in the two conduits being different. The throttle valvesconsist of an axially displaceable, sealed off piston slider 31 and thescrewed-in valve body 32, whose ring channel 33 in connection with thebore 34 facilitates the radial inflow of the oil.

Obstacles are denoted with 35, which cause the formation of a turbulentflow. The reflux valves have the form of simple ball valves; theyconsist of the ball 36, the screwed-in valve body 37 and the adjustable,sealed off stroke limitation 38. The hydraulic medium is introducedthrough the bore 39.

As on account of the resulting high local flow velocities the creationof the necessary resistance in the throttles might lead tounderpressures, to a degassing of the oil, to foam development andconsequently to noise generation, it is suitable to create part of thedamping resistance by means of throttle orifices inserted into the bores34 and 39.

What I claim is:

1. An artificial ankle joint comprising a foot part and a lower legpart, an articulate connection arranged therebetween and a dampingdevice hinged, on the one hand to the foot part and, on the other handto the lower leg part, which damping device comprises at least twohydraulic cylinders with pressure chambers connection conduitsconnecting the hydraulic cylinders hollow pistons having a bottom partand an upper end and hollow chambers filled with storage oilpressure-balancing channels in contact with the surrounding atmosphereand guided as far as the upper end of the hollow chambers aspring-loaded shifting valve arranged between the pressure chamber ofeach hydraulic cylinder and the hollow chamber of each piston.

2. The artificial ankle joint set forth in claim 1, wherein thespring-loaded snifting valve is arranged in the bottom part of thepiston.

3. The artificial ankle joint set forth in claim 1, wherein the lowerleg part is provided with two rollers of equal diameter arrangedsymmetrically in relation to the articulate connection, which rollersare connected by means of a tension spring with the pistons of twoequally dimensioned hydraulic cylinders arranged parallel, the pistonsbeing held in contact with the rollers by means of the tension springs.

4. The artificial ankle joint set forth in claim 3, wherein the pistonsare supported by means ofa tappet on the rollers the tappets havingroll-off surfaces acting against the roller surfaces.

5. The artificial ankle joint set forth in claim 1, wherein in theconnection conduits of the cylinders throttle valves with obstacles forensuring a permanently turbulent flow are installed. 1: l

1. An artificial ankle joint comprising a foot part and a lower legpart, an articulate connection arranged therebetween and a dampingdevice hinged, on the one hand to the foot part and, on the other handto the lower leg part, which damping device comprises at least twohydraulic cylinders with pressure chambers connection conduitsconnecting the hydraulic cylinders hollow pistons having a bottom partand an upper end and hollow chambers filled with storage oilpressure-balancing channels in contact with the surrounding atmosphereand guided as far as the upper end of the hollow chambers aspring-loaded snifting valve arranged between the pressure chamber ofeach hydraulic cylinder and the hollow chamber of each piston.
 2. Theartificial ankle joint set forth in claim 1, wherein the spring-loadedsnifting valve is arranged in the bottom part of the piston.
 3. Theartificial ankle joint set forth in claim 1, wherein the lower leg partis provided with two rollers of equal diameter arranged symmetrically inrelation to the articulate connection, which rollers are connected bymeans of a tension spring with the pistons of two equally dimensionedhydraulic cylinders arranged parallel, the pistons being held in contactwith the rollers by means of the tension springs.
 4. The artificialankle joint set forth in claim 3, wherein the pistons are supported bymeans of a tappet on the rollers the tappets having roll-off surfacesacting against the roller surfaces.
 5. The artificial ankle joint setforth in claim 1, wherein in the connection conduits of the cylindersthrottle valves with obstacles for ensuring a permanently turbulent floware installed.